Electric motor control system



May 16, 1950 R. A. STREMEL ELECTRIC MOTOR CONTROL SYSTEM Filed April 10,1946 INVENTOR. RAYMOND A. STREM EL BY Patented May 16, 1950 UNI-TED STATESS PATENT OFFICE:

ELECTRIC MOTOR CONTROL SYSTEM Raymond Arstrem'el, Concord, Califl,assignor to Yuba Manufacturing Company, San Francisco, -Calif., acorporation of California Application April 10, 1946, Serial No. 660,986

8 Claims. 1 My inventionrelates to a-system of control fortheielectrical' drive of various mechanisms whichrequh'e'zwvide'variati'ons in speed and torque :and frequent reversing.

My; .inventionfhas :a great 'many objects, all of which relate to.increased :efli'ci'ency particularly in respect "to'dred'gingiroperations the broad field of mining.1Morewspecifically,Loneof theao'bjects of: myinventionistheimorerefficient use of direct currentmotor's asprimemoversgwithconstant'torqueaand speed irrespectiveof load, withinthe'horsevpower'rcapacity .of the motors. Another object'is *greateriecon'omyiin the use of electric energy which' is "conservativelyestimated to amount to:1"0'% overrianypther system.

Theinventi'onrpossesses" other objects, some which with the'iforegoingwill "be 'set forth sat length' inrthe lfollowing descriptionwherein is explained that form of the invention which has been. selectedffbr' illustration in the drawings 'a'ccompanyingsan-d. iiformin'g apart of "this specification; :In'said= drawings, oneform of theinvention is shown; but it is to be understood that it; is not: limitedtothat "form; since thezinve'ntion as :setxforth :in the: claimsmaybeembodied in a pluralityiof forms.

In the drawings, the drawingsis a diagrammatic;presentation of thesystem of this :inventionw Oneamethod of speed control in use prior tomy invention, comprises vanalternating current induction motor with-manual or magnetic control1er,-and a banlr'of resistors in thesecondary or rotor circuit tof'the motor. 'Another method of specd-'control" comprises a motor-generatorset which" furnishes variablevoltage to the armatures of the "respective drivin'g 'm0t0rs.-. Theformer method-is "the more-common, but the latter, because 20f itsoperating characteristics, is preferable,=--ialthoughfirst cost andmaintenance :expensei-isgreater. 1

In utilizing the electricalequipment .just'mentioned -vto effectvariable-speed in the alternating current-type, thezcontrollerimay bearranged with 3 :to -=8 steps; the last step egiving the operatingspeed. The :resistors are win the :rotor circuit of the :motor :andmaybe cut-in. or cut: outby: means of :the .control=ler-. The11101501211315 varying speed characteristicswIt -1is ensu-ally notfeasible 1 to ope-rateeattless than 50% "of full speed; althoughthereeis .frequent need for doing so. I

In utilizing the direct current system to effect var-iable-qspeedsin the.direct: current: motor drives, three phase alternating currentpowerflis brought to f thezmotorc of pa; motor-generatortset. A ;gen-:

erator is required for eachof thei'motors onany of the drives.Thegenerat'ors' "however are .all on a common shaft. The:"operatorcontrols the speed from standstill to basicspeed'ofmotor-by varying thefield rheostat on the -:generator; Speeds above basic speeds are-obtainablewirom the same controller through the use of resistanceinserted in the field of the "motor.

The electrical apparatus "and operation just described as constitutingthe practice prior to my invention has many serious deficiencies, whichit is my object to eliminate in-the-presentinvention.

The deficiencies in the alternating :currentmotor,'which it is mypurposetofeliminate, :are several in number which are as'follows:

The available controllable speed range in'insufficient to meetoperational requirements; being limited toa ratio ofapproximately-two--to-one;

The alternating motor drive system is-subject to poor speed regulation,'the speed varying excessively with varying loads.

Theefiiciency oi the-alternating wound-rotor motor system including theexternal 'speed"controlresistor is seriously reduced-bythe losses intheexternal resistor andthis loss is proportional to theextent of speedreduction. -This is an item of particular concern in the bucketlinedrive motor systems which usually consume as much-as 30% to 50% of thetotal energy requirements.

The alternating current wound rotor motors entail the need ofaccelerating relays andmagnetical-ly operatedcontactors for varying theamount of resistance in theexternalspeed-control resistance, and inlarge installationsthis necessitates large and expensive panel boards.

In the direct current motors utilizing motor driven converters, thedeficiencies are: vA generator is required for each motor.All-generators and exciters are directly connected on a common shaftwiththe alternating current driving-motor, which involves considerable spaceand weight, and requires a special base. Maintenance re-= quirements arehigh. Rotating equipmentre quires "considerable attention. An entiremotor generator set must be in operation toefiect functioning of anyindividual drive *attimes when the dredge is not in full course ofdigging operations causing waste of power, considerable-vibrationandtn'oise.

With these deficiencies of the previous system in'mind,-it is thepurpose ofmy'present invention to provide improved electrical adjustablespeed apparatus .ior various drives on dredges Iwhich hasvthei followingimproved characteristics- A wide range of speeds to permit bestoperation in varying formations of ground. A saving of space and weight.An installation which requires less attention and maintenance, and onewhich permits smoother control. An installation allowing operation ofindividual equipment Without operating an entire power generation unit.Self protection against excessive overload condition without openingcircuit breakers. An installation in which the efiiciency of conversionis considerably higher than possible to obtain with motor generatorsets. Installation costs are reduced since no special foundation isrequired. Elimination of vibration other than transformer hum is ob--tained. An installation in which no special ventilation is required.

In broad descriptive terms, the apparatus of my invention comprises anelectronic conversion unit for each drive requiring variable speed onthe motors mentioned above. This will consist of one anode transformer,and a bank of ignitron rectifiers and a direct current motor for eachdrive.

All of the drives in my system are arranged with adjustable speed motorin order to gain the advantages of operating at an optimum speed tomatch varying operating conditions at a greater eiiiciency thanpreviously possible.

The electronic system is arranged with a main anode transformer ofsuffioient capacity to supply all adjustable speed drives. The secondaryof the main anode transformer is arranged for G-phase distribution; andeach motor is provided with its own set of ignitron rectifier tubesconnected to the fi-phase bus. Associated with each motor is also amanually operated controller by which it may be individually controlled.

The starting and variable speed up to basic of each motor is obtained byvarying the voltage to the armature. The field supply is held constantup to and including basic speed, at which time the speed may beincreased beyond basic speed by reducing the voltage to the shunt field.A very low power level type of control equipment is used.

Adjustable voltage input to the motor armature is obtained by varyingthe firing point of a bank of ignitron rectifier tubes. The current usedto fire the ignitron rectifiers is furnished by thyratron gridcontrolled rectifier tubes. The control grid of the thyratron actuatesthe starting of the discharge. By supplying the grid with. a, voltagewhose phase with respect to the anode voltage can be shifted, thethyratron tube will. conduct only after that part of the cycle at whichthe grid voltage reaches its critical value. In other words, a phaseshifting device that can supply to a thyratron, a grid voltage betweenand 180 out of phase with its anode voltage, can thereby control thethyratron output voltage and current from approximately zero to fulloperating voltage.

In the drawin I have illustrated diagrammatically a typical electronicsupply unit and control unit and their circuits, for the operation ofmotor 35. The magnitude of speed and direc tion of rotation of the motor556 is controlled within the 87 arc of travel of its controller handle68 in either direction from its neutral or off position. The controllerassembly consists of two main parts, the master switch section 61comprised of a number of switches, and the potentiometer rheostatsection 63.

The master switch section serves two purposes: first; to controldirection of rotation of the n1otor 36; and second, to control themagnitude of the ignitor current to the ignitron rectifier tubes 4 69,which supply power to the motor armature 36A.

A series of cams "ND, "NE, HF and HG comprising disks rotarilyadjustable to vary the degree and angular placement of the high oractuating face of the cam, is arranged on the shaft 12 to open and closesingle pole switches 13D, 13E, i315 and 13G; and a similar series ofcams MD, ME, REF and MG is arranged on the shaft 16 to operate theswitches llD, HE, HF and ."IG respectively. The two shafts l2 and T6 areconnected for rotation with shaft 18 by the gears 19. The shaft 58 isturned to one side or the other from its central or neutral position bythe controller handle 60.

A change in the direction of rotation of the motor is accomplished bythe automatic transposition of the leads to its armature when thecontroller handle is moved. Cams 'HD and MD in each series operatesswitch 13D and 11D respectively of the associated series of switches forthat purpose at the beginning of the movement of the controller handle.The remaining switches 73E, F and G are connected for forward rotationwhen the controller handle 66 is moved to the left; and the remainingswitches TIE, F and G are connected for reverse rotation when thecontroller handle is moved to the right.

Except for the cam D and switch D in each series of cams and switches,for controlling direction of rotation, the other cams and switches ofeach series are employed to control the magnitude of the ignitor currentto the ignitrons, in the first 30 of movement of the controller lever66. The ignitor voltage is increased as the controller lever is movedthrough its arc of travel, by the progressive shunting of the resistorbank 8|, which is connected in series with the output of rectifier 82and the saturating windings of the saturable reactors 2-3, constitutinga variable impedance. This impedance is in series with the primarywinding of the thyratron anode transformer 84 and the main power supply21 in order that the voltage applied to the thyratron anodes andtherefore the period of conduction of the ignitrons controlled therebycan be varied in a manner presently to become apparent.

After the controller lever 06 has moved the cams 30, all of theresistance bank 8! has been bypassed or shunted out by means of theswitches, resulting in full excitation of the saturable reactors 83,thereby reducing to a minimum the impedance in the supply line to thethyratron anode transformer primary 84 so that the thyratrons 85 givethe required ignitor current to the ignitron tubes 69. Thyratron tubes86 trigger the ignitrons 69 by means of the ignitors 81. The purpose ofcontrolling the magnitude of the ignitor current as described above, isto prolong the life of the ignitors by making the current in theignitors at low motor speed less than that employed in normal operation.

The remaining section of the controller consists of the potentiometerrheostat assembly 68, which concerns the means for varying the speed ofthe motor 36 by varying the voltage supplied to the motor 36. To operatethe motor efficiently at reduced speeds, and fully employ the wide speedrange which is a characteristic of the direct current motor, both thearmature and shunt field voltages are controlled through the meansprovided.

The armature voltage is controlled by a pair of ganged potentiometerrheostats 92 and 93. P0- tentiometer 92 is employed when the controllerleveriizisrmovedatoathecleft; for forwardrspeed of themotor.:Rotentiometeri93.sis:employed@when the; motor is tobe:-:-1'eyersed;;;and thencontroller ever is moved to-ethe right: i:Selection -fo-the potenti-ometer: section 92: or 93 z ishmadebye-meansswitches u -arid 951 ulheswitche's '94rj'and z95wsareoperatedt-mechani'cally byithezshait slurocked by the-armature 98,nwhichais moved 'bY-ithBIiCOlil'rQQR mi of the-reversing magnetic.switch 99.

I when reversing-switch coilI-EQSR is energized by movingicontrollerzlever fifi'to the right andiiclosing switch 'IID,:-thenormal-lyeclosedvcontacts 94 aren openeddthereby, :disconnectin'g theforward potentiometer 92. Attheasameltim-e the normally open contaots95- are: I closedwthus selecting the reverse potentiometer 93. Selectionor the forward I potentiometerrheostat 92 *is automatically made whenztheswitch a coil flR is 'deen'ergized which allows the normally-'closed'-contacts= '94 to assume their normally. closed position.'"'-This same -position' is assumed at all times when the switch coil 98R isdeenergized.

' -The slidersIIH 'anir' I02 of the forward and re--verse=--potentiometers BZ- and I 93 respectively; are '-gang-operatedbyashaft' I 03 on which 2is-fixed gear IM, driven by geai I05 fixed onshaft I8.':":The

I --gears-are in-the:ratio-of-1 to"1.37: respectively, sinceit"is-desirable that -the arc otstravel Di't'he potentiometer armsbeconsiderably greatercthan that of the actuating controller-handle 6B.

To control-the-voltage applied to the armature the potentiomete'r s92-and 93 areuemployed with-the-phase' shift network I961 These controlonly the small amount ofdirect current irom'ethe "rectifier 82;which isnecessary to var the inductiance'of-the six saturable reactors I01 Theprimary winding 'IUSP ofthe: thyratron gri'dztransformal- E08 -is==connected invz-the*phaseushittznetwork -l I! 6 so that the grid-voltageusupplied bycthe secondarywindinghwils can be' shifted inrphase'with respect to the phase of: I the anode voltage applied to=thethyratron tubes 86;:- By thislag or delayed-firing in eachcycle;the-:thyratrons 86 willcorrespondinglydelay the triggering zorithe-'---'ignitrons.- Therefore the averagei yoltageioutput will be lowand-the-armature'lwillxoperatev at only a fraction-of the -basicaspee'd'ofi theunotor.

The potentiometers SZ a'nd 93 areso arranged that their resistancevalues are cut outiwlithin an: angularmovementiot'sliderszillkand Hi2.respec- -=tively-, thereby applying 'irated armature-,yoltage "acrossthe motor-armature; resulting in*=:..opera- 'tion of the motorat-basic-speed if ratcdvoltag is applied across motor'shuntefield 38. a

It'shOlfld "be =und'erstood'zthat as: theislidera I t I and; I I) 2 Dfsthe-:armaturei; control -:potentiometers 92 and =93? arezadvancedtrfrominentraliposition to :1 2 za -sposition" 7a0afromi neutral; thelresistorxsegment or:vz'resistanc'z'ee I09 of": thegpotentiometers will begradually 1- cuti out ;i:and-:rthatzthe effective :resistancesofiereditoi. the.icircuitfor: phase shiftingpur- *poses will be. :from:maximum at neutral. position to nothing: at a. point '7.Q?-or;more:from-neutralpositionicr- -Thex:potentiometersv: are sor-zconstructed.thatrthesliders travel beyond 70;without-chang- ,ing zresistance-valuebyallowing the sliders to ride r- I. .over a nonresistance, strip I Iit: of. copper or-other metal possessing-reasonablyrgoodiconductance.

the double? 'pole- :doublecthrowliauxiliarycontrol 6 -.=,1I'l:6ofetheirheostat is mechamcally'iactuated to move through the samesangleas -the :sliders IUI and; I02 off-potentiometer's Stand .93respectively, whiclrcontrol theiarmature voltage; As thexsliderIHtmoves: through 70 omeitherside ofmeutral, :it'. ridesons'ascopperistripi I I8-,itl1us:not affecting .:.a.characteristicsorroutputsz During this time the irjvoltage output from. the-fieldsupplyunit 39;.wi11 be at ratedvalue and. constantyand thelivoltage outputfrom the ignitrons to thezmotorarmature .Is 36A will also be atitsvrated. value, sorthat the I motor. will operate at basic-speed!Therheostat ;Ii,I :is used toextend thesspeedorangebeyond 'basicr-'motorspeed by taking advantage ofr the l5: characteristic of the. :directcurrent motor-the i -speed of which can be increased from two toifourtimes its-basic-speed when its field excitation is rel-weakened? Thisextra speedrrfeature is often a sgreat'advantage, especially in dredgemanagement,=whcrein manyxoperations can benexpedited when necessary 'Inmost cases-motor speeds will be selected totoperate normally nearthe-basic speed'of mot0r,"but the adjustable speed features of: myinvention may be" employed to meet vary- 25 ing. and unusual operatingconditions either above 1 orbelow the-basic speed.

As thev rheostat: slider I I 8- leaves the conductingstrip H8,itengages-the remaining 50 of travel'of one or the other ofthe resistorsections 39 II9,- thus inserting an increasing-amount of resistance in.the-phase shifting circuit including -"eapacitors Stand 91a "and. thesecondary I'Z'ISG of the transformer I 2 I: -inserting more and more:resistance' in this circuit causes aphaseshift in grid I22 of thethyratron l I3, to a point where its output approaches zero, but leavingthe 'associated thy-ratron H2 operating; Thyratrons- H2 and l 22-areenergized by-alternate partsof tapped secondary I2 ISA so-that full waverectification is 10 obtained when both thyratrons are-operative.""Wh'enthe output of thyratron I22 isreduced the average voltage isreduced 'untiI at the-point M wherethyratron' I22 is cut-off,rectification is half wave; and 'theaverage voltage is: consider- 5 ablyreduced. This arrangement is of particular 1 value forthereason'that thereduction of voltage for the-motorshunt field is definitely limited to a*safe'value.

To-secure refinements of" circuit, *variou's -filse ters, condensers;resistors; reactors,- transformers, and'other-devices may be suitablyemployed. I "have omitted-them-from this descriptionin order to avoidunnecessarily complicating the drawings and: description of myinvention. 55; 1 Summarizing'theaboveexplanation, it'can be "'seenthat'as. the 'operatormovescontroller lever 66 in either direction,the'motor -35.Wi11St3;1l7 a i- Slow. rotation forwardly or in reverseas. deter- .i mined by directionof movement of the controller l i'lever,66,.and thersclosing of one of the "switches 13D or" 11D bythe..cam ,IIDorfMD respectively. t-Themotorswillhthen gradually and smoothlyinll-creaseitsspeed as the operatoradvances the conttrollerleverr .Themotor speedwill be nearly prouportional tonthelsetting of the"controller lever; .-sand-thew.operatorscan vary the speed ashis'judggmentadictates to; suit varying operating condi- 1 tions.

., trolled by thesrheostat I It, and connected to-grid .rscontrolledgthyratrons; I I 2 sand-i1 I 3. i Theerheostat operatedby-theacontrollerihandle 66;;shaft I8, ears: I-Bfiaand- I I41: (intherratio of111.3 -7 .to -1-).-and

shaft- I I5. Through; theseiconneotions theslider:

circuits through .lines I51 and I52 is rcompleted, andithe forwardswitch0011691 is energized The ii ;circuit 15 ITI 52' :iswa- 10w.voltagedcontrol, supply derived from the-.transforrnen I 53, energizedfrom 1531 1119.", main vy3-phase J alternating current supply, 2 I.

7 Branch lines I54 and I55 extend to the primary I 2 IP of thetransformer I2 I.

At the first instant of movement of the controller handle 66 and shaft78, the slider Edi of the potentiometer 92 sliding along the resistorsegment I09, cuts out a small amount of the total resistance existing inthe potentiometer 62 and the phase shift network I06, the latterincluding in series connection a saturable reactor i8? and a fixedresistor I58 for each of the six phases; This progressive lessening ofresistance Q99 causes a correspondingly small decrease in reactance ifand therefore in the phase lag, so that the firing of the thyratrons 86begins, to be followed successively by the ignitrons 68. The closing ofoi;- cuit I5I-I52 energizes the coils 88F of the magnetic switch 99,pulling over the armature W8 and rocking the shaft I 6| to close all ofthe switches, I62 and H63 in the motor armature lines I64 and I65, andswitch 161 in the line I88 to the magnetic brake i653 so that the brakeis released. It will be noted that the righthand group of the switchesactuated by shaft it; are connected in parallel respectively withcorresponding left-hand group of switches linked to shaft 9.1. These ofcourse, come into action when. the controller handle is moved to theright to secure reversal of the motor. Coincident with the closing ofswitch 73D, another switch 73151 is closed by the cam 'IIE to establisha circuit in lines I and I'll, shunting out a portion of the resistorbank 8|, which is disposed in the direct current circuit from therectifier 82 to the saturable reactor 83. Another network is in the lineI'I2I'I4; and is connected to the pot-en tiometers 92 and 93 by line575, which in turn are connected by line I16 to the rectifier side ofline I13. With continued movement of the controller handle, the cam 1 IFcloses the switch 18F in the circuit I'I0-II8 to shunt out the remainingportions of the resistor bank 8|. Simultaneously with the turning of thecams HE and ill to close their associated switches, the slider I8! ofthe potentiometer 92 has advanced to remove more of the resistance I89which effects a lessening of the angle of lag in the phase shiftingnet-- work I06, thus causing thyratrons 88 to fire earlier in eachcycle. The lessening of the am gle of lag advances the phase of thevoltage in the primary IDBP, which is accompanied by an advance in phaseof the voltage in the secondary IIJ8S resulting in an earlier firing ofthe thyra-- trons.

With the further movement of the controller handle 65 through anadditional angle of 10 cam IIG closes the corresponding switch 13G,establishing a shunt circuit in lines II0I'IS around the resistor bank8|. At this point saturable reactor 83 has decreased to the value atwhich maximum or rated output is applied to the thyratron anodetransformer 84. During all this time the current through line Il2-I'I4I15-! "i6 and the network I06 has been continually increased as the armIDI eliminates the resistance I 09 in potentiometer 92. At a point wherethe arm has cut out all the resistance I09, the network Ill6 has shiftedthe grid voltage of the thyratron tubes 86 into the minimum angle of lagand to such a value as to give the rated voltage from the ignitrons 69to the motor armature 36A. At this value, the basic speed of the motorhas been reached, and irrespective of normal rated load, the motor willcontinue at this speed. If the motor is now to be stopped, thecontroller handle is moved back to neutral, breaking the circuits andallowing the spring operated brake I69 to set and bring the motorquickly to rest.

During the movement of the controller handle forwardly the slider II6 ofthe rheostat III has moved in contact with a copper strip IIB, with noeffect on the circuits, I8I-I82 connecting it to the thyratrons H2 andH3, which control the motor shunt field 38. At the time the motor hasreached basic speed, the controller handle is at an angle of 70 with thevertical; and if it is pushed still further to the left, the slider II6enters upon the resistor segment II9, introducing gradually increasingresistance into the circuit. It will be recalled that the primary I2IPhas been energized through the lines I54 and I55, the rated voltage tothe shunt field 38 having been at the maximum point through the actionof the secondaries IZISA, I2ISG and IZISF and thyratrons H2 and H3. Withthe gradual building up of resistance in the line IBI, a phase lag iscreated in the voltage supplied to the grid 122 of the thyratron tube II3 by the secondary IZISG of the grid transformer. As a result thevoltage to the shunt field 38 through line I83 connecting it to thecenter tap of the filament transformer secondary iZiSF, and through lineI84 connecting it to the anode transformer secondary IZISA, isprogressively reduced with corresponding lessening of field excitationto allow the motor 36 to speed up beyond its rated basic speed. Themaximum speed is attained when the slide IIB has reached the end ofresistor segment H9. At this point, only tube I I2 remains in operationto prevent complete loss of the field excitation and I the motor runningwild.

Returning the controller handle 66 toward neutral position, firsteliminates resistance in the potentiometer I I I, and restores thenormal rated shunt field voltage, bringing the motor speed down tobasic. Then as the controller handle approaches the neutral position,the angle of phase lag in voltage supplied to the thyratrons 86 andcaused by the network I66, gradually increases as the resistance in thepotentiometer 92 returns to maximum, and the resistor bank is reinsertedin the circuit through the saturable reactors. This reduction in voltageinput to the armature, gradually reduces the motor speed and finallybrings it to rest.

I claim:

1. An apparatus for controlling the speed of a direct current motorcomprising a three-phase alternating current supply, an anodetransformer having a secondary arranged for six-phase distribution, aniignitron tube for each phase and to the anode of which the phase isconnected, said ignitron tube having a cathode connected to one side ofthe motor armature, a neutral bus connecting the other side of thearmature to the neutral of the secondary of the transformer, a secondanode transformer having a primary winding and a secondary winding, aplurality of controllable first impedances connecting the primarywinding to the alternating current supply; said secondary being arrangedfor six-phase dis tribution and connected to the ignitron cathodes, athyratron tube for each phase of the second transformer secondary and tothe anode of which the phase is connected, each thyratron tube having acathode connected to the ignitor of the ignitron of corresponding phaseand means including a plurality of controllable phase shiftingimpedances for supplying the grid of each thyratron tube with voltage,and control means for simultaneously progressively decreasing the firstimp'da "e's' to -increase the thyr'atron anode voltage" and. advancingthe phase of the grid excitation wherebyith'e igniton current andignitron energy outputlto the motor. armature are-simultanecuslyincreased.

2. An apparatus for .controllin'gthe lspeed of a direct currentniotorcomprising three-phase alternating'current supply a first anodetransformerhavin'g 'a secondary (Winding. arranged forsix-phaseldistribution, an ignitron tubenior each phaseandto theanode ofwhich the phase is connected, saidlignitrontube having a cathodeconnected to one side of the-motor'armature, a neutralbus connectingtheother side-of the arm'atureto the neutral of. the secondary of the inga-iprimary anda secondary and having its secondary arrangedfor ix phasedistribution; a gridcontrolled gaseous discharge tube having a cathode,a controlgrid am n anode for each phasesof. the second trans-formersecondary, and to the anode of which the phase is connected and to thecathode o'f which .the ignitron ignitor of H transformsr, a second ianode transformer hav- I corresponding phase is connected, said secondthe anode-of which the phase is connected, said ignitron tube having acathode connected to one side oi the -motor-armature,--a neutral busconnecting.the-othersideof the armature to the neutral of the secondaryof the transformer, a second anodeltransformer having aprimary and asecondary;--controllable--reactive means connectin-g the primary to thealternating currentsupply saidasecondary-being arranged for sixphasedistribution and connected-tothe ignitron positivebusyathyratron'tubefor each phase of the second transformer secondary,and to the anode of which the phase 'is connected, each thyratron tubehaving a cathode connected to the ignitor of the ignitron ofcorresponding phase, means including a controllable phase shiftingcircuit for supplying the grid of each thyratron'tube with voltage andunitary control means-iron increasing the thyratron anode voltageandsiinultaneous1y shifting the phase of the grid current relative? tothe phase of the anode currenteto-vary the firing of the thyratron tube.

4. In an adjustable speed motorsdrive, a source:

of polyphase' alternating current; a' first po1y-.

phase transformer having primary and secondary windings, .*the primarywindings *being connected to the-isource..ofalternating currentflanclthe secondaries being star connected, a plurality of ignitrons eachhaving a cathode, an anode, and an ignitor, the anodes being connectedrespectively to the free ends of the transformer secondaries, and thecathodes being connected together to provide a unidirectional currentterminal; a second polyphase transformer having primary and secondarywindings, the primary windings being connected to the source ofalternating current, the secondary windings being star connected andeach pair of adjacent free ends being connected together by a saturablereactor in series with aresistor, aplura'lity'of thyratrons,

one for each phase and each having a cathode, anode, anda ontrol grid,each cathode being connected in series with the ignitor of the ignit- 1ron of like phase; a grid input transformer for each thyr'atron havingprimary and secondary windings, the primary winding being connectedbetween the common terminal of the star connected windings of the secondtransformer secondaryi and the junction between the resistor andreactorlocated between the secondary winding of th secondary transformerof respective phase and the adjacent succeeding winding, the

secondary oi the grid input transformer being:

connected to the respective thyratron grid, a third polyp'nasetransformer having primary and secondarywindinga-the primary windingsbeing i connected to the source of alternating current through saturablereactors, and the secondaries being star-connected, the free ends of thesecondaries being connected to the respective anodes I of saidthyratron, uni-control means for control'iing'the amount of saturationin said satur-s v able-reactors whereby the voltage applied totheanodesof the thyratrons is controlled as to amplitude and phase so asto control the on and on condition of the ignitrons and define theextinguishing time-of each firing and the phase of the voltage appliedto the grids of the-thyratrorss can be varied to control the initiationtime of each firing of the thyratrons so that the output voltage-andcurrent of the ignitrons canbe controlled smoothly from zero to maximum.

5. Motor control means for controlling the speed'torque and direction ofadirect current 1 motor comprising a source of alternating currentand-an ignitor controlled rectifier source of pulsating direct current,reversing switch means i connecting-the motor armature to said source,ignitor exciting means comprising a pluralityof thyratrons,- firstsaturable reactors including--1- control windings for controlling thepotential of the thyratron anodes and the phase with respect to thesource of alternating -current;='second saturablereactors includingcontrol windings -"for controlling the phase of excitation of thethyratron gridswithrespect to the'anode excitation, saidfirst-and'second saturable reactors having sufficient 'reactance todecrease the thyratron" anode-potential and delay the grid excitation tothe non-firing condition, a source of direct our rent-ffor the motorfield comprising a pair of second t'l'iyratrons'a'source of directcurrent, a

series resistance connecting the first 'saturable re actor'controlwindings inseries with said direct current source, a potentiometerconnecting said second -saturable reactor control windings in serieswlthsaid direct current source;- one of said thyratron's "having a phaseshifting 'grid excitation control including a rheostat whereby-itsoutput is adjustable from maximum to zero; said motor" control meansincluding first means for progressively selecting'the position of thesaid reversing"switchfaplurality of switchessequen tially operated toprogressively short out portions of said series resistance, a mechanicalcoupling to said potentiometer to simultaneously progressively decreaseits resistance to advance the phase of thyratron grid excitation andmechanically coupling means for progressively decreasing the output ofthe field supply source after the switches are closed and saidpotentiometer has been operated to the minimum resistance value wherebythe direction of operation, the turning 11 on, and the torque and speedof the motor are progressively selected.

6. Control means for controlling the direction and speed of a motorcomprising an alternating current source, a first transformer having aprimary winding connected to said source, and a plurality of secondarywindings having a common junction and free ends, a plurality ofignitrons and means connecting each of said secondary windings torespective anodes of said ignitrons, a second transformer comprisingprimary and secondary windings, first saturable reactor means connectingsaid second transformer primary winding to said source of alternatingcurrent and including control windings, a source of direct current, avoltage divider connected in series with said source of direct currentand said saturable reactor control windings, a plurality of camcontrolled switches having a normally open condition and connected inshunt with respective portions of the voltage divider, a controllerhandle mechanically coupled to a common shaft, a plurality of cams, saidcams being juxtaposed to said cam controlled switches and actuated bysaid common shaft to successively close the switches in sequence inresponse to progressive motion of said controller to therebyprogressively raise the second transformer secondary voltage and advanceits phase with respect to the ignitron anode potential, a thirdtransformer comprising primary and secondary windings, said secondarywindings having a common junction, a plurality of networks comprising aresistance and a second saturable reactor connected between adjacentphase windings of the third transformer, a plurality of thyratronshaving their cathodes connected to respective ignitors of the ignitrons,their anodes connected to said second transformer secondary windings andtheir grids coupled through transformers having primary windingsconnected between the secondaries common junction and respectivejunctions of the aforesaid saturable reactors and resistances, saidsecond saturable reactors having control windings, a rheostatmechanically coupled to the controller handle and connected in serieswith said direct current supply and the control windings of the secondsaturable reactors, whereby motion of said controller handleprogressively closes said cam switches to raise the thyratron anodepotential and thereby determine the potential applied to the thyratronanodes, and simultaneously the resistance 01 the rheostat isprogressively reduced to reduce the lag in thyratron excitation tothereby exercise uniform control in the ignition potential and effectivecurrent, a motor armature connected between the first transformersecondaries common junction and the ignitrons, to thereby be closelycontrolled as to impressed potential and effective current.

7. An apparatus for controlling the speed of a direct current motorcomprising an alternating current supply, an ignitron tube having acathode, anode and igniter electrode, the anode being coupled to oneside of the alternating current supply and the cathode being connectedto one side of the motor armature, the other side of the alternatingcurrent supply being connected to the other side of the armature; athyratron having an anode, cathode and grid, a thyratron anodetransformer having a primary winding and at least one secondary winding,a controllable impedance connected in series between the primary windingand the alternating current supply, the secondary winding beingconnected across the thyratron anode and the ignition cathode, meansincluding a phase shifting impedance connected to the thyratron grid forsupplying the same with voltage, and a manual controller forsimultaneously and progressively decreasing the first impedance toincrease the thyratron anode voltage, and advancing the phase of thethyratron grid excitation whereby the igniter current and ignitronenergy output to the motor armature are simultaneously increased.

8. An apparatus for controlling direct current power over a wide rangecomprising an alternating current supply, at least one vapor dischargedevice having a cathode, an anode and an igniter electrode, the anodebeing coupled to one side of the alternating current supply and thecathode being connected to a positive polarity output terminal, theother side of the alternating current supply being connected to anegative polarity output terminal; at least on thyratron, the thyratronhaving an anode, a cathode and a grid; means connecting the cathode ofthe thyratron to the igniter of the vapor discharge device, meansincluding at least one controllable first impedance for impressingpotential from said alternating current source on the thyratron anodeand means including a phase shifting second impedance coupling thethyratron grid with said alternating current source, and a controllerfor simultaneously and progressively decreasing the first impedance toincrease the thyratron anode voltage, and advancing the phase of thehyratron grid excitation whereby the igniter current and vapor dischargedevice energy output to the load terminals are simultaneously increased.

RAYMOND A. STREMEL.

REFERENCES CITED The iollowing references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 811,683 Yeoman Feb. 6, 19061,403,260 Ludlum et a1 Jan. 10, 1922 1,408,758 Meyer Mar. 7, 19221,426,123 Stoekle Aug. 15, 1922 1,603,137 Meyer Oct. 12, 1926 2,157,888Dawson May 9, 1939 2,259,293 Cox et al Oct. 14, 1941 2,294,709 Bechmannet al. Sept. 1, 1942 2,312,117 Moyer et al. Feb. 23, 1943

